The \(X(3872)\)  resonance has the same quantum numbers as \(\chi _{c1}(2P)\)  (i.e., \(J^{PC}=1^{++}\) )
but with a much lighter mass than potential quark model predictions. Its mass is close to the \(DD^*\) 
threshold and makes it an ideal candidate for the \(DD^*\)  hadronic molecule. Various scenarios have been
discussed in the literature for which recent reviews can be found in Refs. [1]}, [2]}, [3]}, [4]}, [5]}. It is now broadly accepted that the \(X(3872)\)  has both a
long-ranged molecular wave function and a short-ranged compact \(c\bar{c}\)  component [6]}, [7]}, [8]}, [9]}, [10]}.
It can be viewed as the mixture of the \(D\bar{D}^{*}+c.c.\)  molecule and \(\chi _{c1}(2P)\)  combined by a
unitarized strong \(S\) -wave interaction  [6]} (see e.g. Ref. [3]} for a detailed review).
According to other authors the \(X(3872)\)  can be interpreted as as \(c\bar{c}\)  core plus continuum
(meson-meson) components, like \(D\bar{D}\) , \(D\bar{D}^*\) , and so on as in
Refs. [7]}, [8]}, [9]}, [10]}.
